1. Field
The embodiments discussed herein are related to control of a tap coefficient of a transversal filter used in an electronic dispersion compensator. More particularly, the embodiments herein are related to control of a tap coefficient of a transversal filter performing waveform equalization of an electrical signal demodulated in an optical receiver apparatus.
2. Description of the Related Art
Research concerning differential quadrature phase shift keying (hereinafter referred to as “DQPSK”) is actively carried out in recent years. The DQPSK is used as a communication method for improving the efficiency of usage of the frequency in an optical transmission system. Compensation for such dispersions is performed in an optical communication system since waveform degradation occurs because of chromatic dispersion and/or polarization mode dispersion of optical parts, such as an optical fiber and an optical amplifier Japanese Unexamined Patent Application Publication No. 2007-325095 discloses a transmission system using an electronic dispersion compensator to perform dispersion compensation of a reception signal modulated by the DQPSK method.
It is necessary to adjust the settings of the tap coefficients as soon as possible if the current settings of tap coefficients become inappropriate for the current situations because of a change in the situations, for example, a change in the characteristics of transmission lines and/or transmitter-receiver apparatuses. With the increasing bit rates of optical communication systems, it is required to improve the responsiveness of adaptive control of the tap coefficients to the change in situations and to reduce the range in which the inappropriate settings of the tap coefficients affect data as much as possible.
Furthermore, automatically performing variable control of the tap coefficients of transversal filters can cause the amplitudes of signals output from the transversal filters to exceed the input rating ranges of downstream elements.
An apparatus and a method of the present invention are provided to resolve the problems involved in the variable control of the tap coefficients of a transversal filter provided in an electronic dispersion compensator in an optical receiver apparatus performing waveform equalization of a reception signal by using the electronic dispersion compensator.